Redox controlled biogeochemical processes affecting arsenic solubility down a sediment profile
Location
Eccles Conference Center
Event Website
https://water.usu.edu/
Start Date
3-30-2011 10:20 AM
End Date
3-30-2011 10:25 AM
Description
Arsenic concentration in groundwater throughout Cache Valley exceeds the drinking water limit. Previous studies of aquifer solids collected from an area near the Logan landfill revealed that the arsenic in the groundwater is from geologic sources. In order to investigate the distribution of arsenic along a vertical profile and probe the possibility that primary arsenic minerals deposited on the soil surface are the source of arsenic deeper in the profile, five cores, consisting of vadose zone, redox transition zone and saturated zone solids, from the soil surface to 1.8 m were collected from the same area. Geologic As was not confined to the deep aquifer solids but was also in the surficial materials; total As ranged from 2,000 IJg/kg to 17,000 IJg/kg. Chemical extractions shown that As in the surface soils was associated with crystalline iron oxides and sulfides. As-sulfide minerals may be continuously deposited via the weathering of the Salt Lake Formation which contains volcanic rocks along Wasatch Range or leaching of As containing minerals from the Bear River Range. Although As(llI) is the dominant species in primary minerals, oxidation processes at the soil surface will produce As(V). An increased was observed in the proportion of As associated with iron oxides down the profile. Arsenic leached from the surface soils is retained by surface sorption or co-precipitation with these iron oxides. Arsenic then accumulated at the boundary between the redox transition zone and the saturation zone. This accumulation may be due to the reformation of arsenic- sulfides under sulfate-reducing conditions. Microcosm studies using the depth aquifer solids indicated the solubilization of As from some of the aquifer solids were correlated with Fe reduction with or without glucose addition, while other processes controlled As solubilization in solids from different locations within the study area. Bacteria carrying arsenic respiration reductase coding gene were proved to widely exist in this aquifer system. To understand the behavior of geologic arsenic in this region is important because the similar process may also affect other regions in northern Utah due to the similarity in geologic settings.
Redox controlled biogeochemical processes affecting arsenic solubility down a sediment profile
Eccles Conference Center
Arsenic concentration in groundwater throughout Cache Valley exceeds the drinking water limit. Previous studies of aquifer solids collected from an area near the Logan landfill revealed that the arsenic in the groundwater is from geologic sources. In order to investigate the distribution of arsenic along a vertical profile and probe the possibility that primary arsenic minerals deposited on the soil surface are the source of arsenic deeper in the profile, five cores, consisting of vadose zone, redox transition zone and saturated zone solids, from the soil surface to 1.8 m were collected from the same area. Geologic As was not confined to the deep aquifer solids but was also in the surficial materials; total As ranged from 2,000 IJg/kg to 17,000 IJg/kg. Chemical extractions shown that As in the surface soils was associated with crystalline iron oxides and sulfides. As-sulfide minerals may be continuously deposited via the weathering of the Salt Lake Formation which contains volcanic rocks along Wasatch Range or leaching of As containing minerals from the Bear River Range. Although As(llI) is the dominant species in primary minerals, oxidation processes at the soil surface will produce As(V). An increased was observed in the proportion of As associated with iron oxides down the profile. Arsenic leached from the surface soils is retained by surface sorption or co-precipitation with these iron oxides. Arsenic then accumulated at the boundary between the redox transition zone and the saturation zone. This accumulation may be due to the reformation of arsenic- sulfides under sulfate-reducing conditions. Microcosm studies using the depth aquifer solids indicated the solubilization of As from some of the aquifer solids were correlated with Fe reduction with or without glucose addition, while other processes controlled As solubilization in solids from different locations within the study area. Bacteria carrying arsenic respiration reductase coding gene were proved to widely exist in this aquifer system. To understand the behavior of geologic arsenic in this region is important because the similar process may also affect other regions in northern Utah due to the similarity in geologic settings.
https://digitalcommons.usu.edu/runoff/2011/Posters/28